1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for handover in a wireless communication system.
2. Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
A closed subscriber group (CSG) is introduced to provide better quality of service by allowing limited access only to a specific subscriber. A base station capable of providing a CSG service is referred to as a home eNodeB (HNB), and a cell providing a licensed service to subscribers of the CSG is referred to as a CSG cell. Basic requirements of the CSG in 3GPP are disclosed in 3GPP TS 22.220 V1.0.1 (2008-12) “Service requirements for Home NodeBs and Home eNodeBs (Release 9)”.
A handover to a CSG cell is called inbound mobility. In order for a user equipment (UE) to further effectively perform the handover to the CSG cell, the UE and a network share proxy information. For the inbound mobility, the UE sends to the network the proxy information for reporting that a member CSG cell to which the UE belongs as a member exists nearby.
The UE and the network share the same proxy information always. Therefore, if the proxy information changes, the changed proxy information needs to be sent by the UE to the network.
When a serving cell changes due to the handover, the UE retransmits all of the old proxy information to a new serving cell. However, many radio resources may be required to retransmit all of the old proxy information.